1. Field of the Invention
The present invention relates to an endless belt used for a belt-type band sheet coiling tension applying apparatus which applies a uniform and sufficient tension to each slit band sheet without generating scratches on the surface of the band sheet when the band sheet after slitting is recoiled, in a slitter line for slitting a wide metallic band sheet into a plurality of band sheets along the longitudinal direction of the band sheet or a trimming line for cutting off ear portions at both ends of the band sheet to slit the band sheet into a band sheet having a specific width, and specifically, to an endless belt with slits capable of applying a sufficient coiling tension without any relative slip between a band sheet and the endless belt even in a state when rolling oil or rustproof oil has adhered to the surface of the band sheet.
2. Description of the Related Art
As for patent techniques utilizing any difference in frictional coefficient between a surface and back layers of an endless belt for belt-type band sheet coiling tension applying apparatus, these are disclosed in JP56-A-82755 and U.S. Pat. Nos. 3,769,730, etc. In applications of these inventions, synthetic-rubber-based and synthetic-resin-based materials having a large frictional coefficient are utilized for the surface layer material on the side touching the metallic band sheet, and a synthetic-fiber-based material, such as polyester having a small frictional coefficient is utilized for the back material. However, in a band sheet on the surface of which oil is applied, a frictional force is remarkably lowered due to an oil film on the surface of the band sheet, and the band sheet and the surface of the endless belt slips, and the belt does not rotate in synchronization with the coiling speed of the band sheet. Thus, scratches are not generated on the surface of the band sheet, or sufficient tension is generated. Therefore, these techniques are not satisfactory when oil adheres to the band sheet.
Thus, new techniques are shown in Prior Japanese Patent No. 2701004 in which an endless belt is composed of three-layer different materials of an outer layer, an interlayer, and an inner layer, and the frictional coefficient on the back side of the belt is made small such that the interlayer is made to contain lubricating oil, and the contained oil is oozed out to the back side of the endless belt by providing guide through holes for lubricant passing through the interlayer to the inner layer, and a technique in which an oil film is partially cut by providing irregular patterns on the outer layer of the surface of an endless belt to strongly push convex portions against the surface of the band sheet, and the difference in frictional coefficient with the backside of the belt is retained by increasing the frictional force between the belt and the band sheet. Actually, however, these techniques are not practical because the oil film of the band sheet on which oil is applied cannot be removed simply by providing holes in the flat belt shown in Japanese Patent No. 2701004, and only the endless belt made of a surface layer material having a number of dents is put into practical use.
However, in recent advances of a rolling technique of metallic band sheets or the recent diversification of the surface treatment of band sheets or for press molding as a post step, use of band sheets which are easier to slip are increasing. Moreover, rustproof oil, or lubricant for press working is applied in many such band sheets that are easy to slip. Even if such a special endless belt as mentioned above is used, the coiling speed of the band sheet has a limit up to about 50 m per min. In coiling at higher speed than the said coiling speed, the oil film cannot instantaneously be cut, and the frictional force between the belt convex portions and the band sheet becomes insufficient. As a result, at the present time, productivity significantly is limited due to the occurrence of the slip of the endless belt.
In the belt-type coiling tension applying apparatus of this Japanese Patent No. 2701004, a pressing mechanism on which a pair of upper and lower endless belts are mounted is driven, and a band sheet is nipped in a sandwiched manner by the upper and lower endless belts. Moreover, a coiling tension is adjusted by increasing and reducing the pressure of a pressure cylinder annexed to the pressing mechanism. However, even if the pressure of the pressure cylinder is raised, the surface of the endless belt completely cannot remove the oil film of the band sheet on which oil is applied. Therefore, when the thickness of the band sheet is relatively large, tension becomes insufficient. Alternatively, when the thickness of the band sheet is relatively small, convex projections on the surface of the endless belt is strongly pushed against the band sheet. Therefore, concavely dented deformation is caused in the surface of the band sheet. Thus, this technique cannot be adapted to a relatively thin band sheet.    Patent Document 1: JP56-A-82755    Patent Document 2: Japanese Patent No. 2701004    Patent Document 3: Japanese Patent No. 3769730
In the prior techniques, when some or the entire belt does not rotate in synchronization with the coiling speed of the band sheet due to an insufficient frictional force on the surface of the endless belt, slip marks are attached to the surface of the band sheet. Therefore, an undesirable defect occurs simply by coiling operation, and consequently, products are not obtained. Thus, the coiling speed is lowered to 50 m or less per min, and operation is barely performed. Hence, an endless belt which rotates in synchronization with the bans sheet speed even at 200 m/min or 300 m/min which is the highest speed inherent in a line and which has no concern about slip marks or the like is desired (the coiling speed is not raised).
The oil film is removed by the convex portions of the surface layer member of the endless belt, and the oil removed into the cavities between the convex portions is collected. In this regard, since escape holes for oil exists in some of the cavities, the oil escapes to the back of the belt. However, since the oil in the cavities with no oil escape holes is sealed, and the oil film remains, slip is likely to occur. Therefore, application to a relatively thick band sheet which requires a large coiling force cannot be made, thereby limiting the thickness of a band sheet to be applied (cannot be applied to a thick band sheet).
Alternatively, since the surface pressure in the convex portions becomes high in an endless belt on the surface of which cavities or irregularities exist, a relatively thin band sheet is nipped and held by the irregular surface of the belt. Therefore, there is a drawback in that irregular marks are attached to the band sheet. Also, when the pressing force of the belt is lowered in order to avoid this, the coiling tension becomes insufficient, becomes nonuniform or slip occurs. As a result, a band sheet coil is not securely and firmly coiled, and coiling of the band sheet coil may collapse (cannot also be applied to a thin band sheet).
Although the previous prior techniques as described above depends on the frictional force between the surface of the band sheet and the surface of the endless belt, there is instability that the oil film of the surface of the band sheet coil cannot completely be removed by any means. Although this unstable factor needs to make the frictional coefficient between the band sheet and the surface layer material of the endless belt larger than the frictional coefficient on the backside of the endless belt, there is a limitation on the frictional force in a state where an oil film remains.
Meanwhile, the surface of the band sheet has a surface roughness (refer to FIG. 17) of several microns formed by a rolling mill roll during the continuous rolling manufacture of the band sheet coil, or plated fine irregularities of the surface of the band sheet (refer to FIG. 18). Although the surface roughness of a metallic band sheet varies depending on the applications of the band sheet, steel bands used for automobiles or home appliances are finished to a moderate surface roughness in consideration of image clarity or the like after press molding or finishing as a post step. In this case, since the maximum roughness is approximately 1 μm to 5 μm, and the peak and valleys of the irregularities spread on the entire surface of the band sheet, it is general that the pitch number PPI (stands for Peaks Per Inch and represents the number of peaks per 1 inch (length)) of peaks of the irregularities is approximately 100. That is, peaks with 100 (number of peaks)/25.4 mm (length), i.e., four per 1 mm (length) and a height of several microns continuously are repeated in the irregularities on the surface of the band sheet.
In consideration of the above-described problems, the invention was contrived in order to solve the problems, and the object of the invention is to provide an endless belt with slits for a belt-type band sheet coiling tension applying apparatus allowing positive application of a coiling tension without any relative slip by providing a number of closely notched slits with a predetermined depth at predetermined intervals on the outer surface of the endless belt in order to focus on the surface roughness of several microns of the surface of the band sheet or plated fine irregularities of the surface of the band sheet, and catch micron-size peaks and valleys of the surface of the band sheet, thereby catching the band sheet on which an oil film remains as fine convex portions of the surface of the band sheet bitten into the slit portions, respectively, and simultaneously sucking the band sheet on which an oil film remains as the slit portions which are brought close to each other and have no gap are pulled to the fine convex portions of the surface of the band sheet which have bitten thereinto, and are deformed to form cavities to generate negative pressure, and all of a number of the slits of the endless belt touching the surface of the band sheet serves as a vacuum pump.